A scanning Michelson interferometer is the type of instrument wherein an input beam of radiation, which is to be analyzed spectrally, is divided into two subbeams by a beam splitter, one subbeam being reflected back to the beam splitter along a path of fixed optical length and the other subbeam being reflected back to the beam splitter along a path of variable optical length for recombination with the first subbeam to form concentric circular interference fringes on a radiation detector. The variation in detector output as a function of the varied path length can be analyzed by suitable known Fourier transform methods to yield the spectrum of the input radiation beam.
Various devices have been used for varying the optical path length of one arm. For example, UK patent application GB No. 2162334A published Jan. 29, 1986 and an article entitled "RAPID SCAN PHASE MODULATOR FOR INTERFEROMETRIC APPLICATIONS" by D. J. Campbell, P. A. Krug et al appearing in Applied Optics, Vol. 20, No. 2, Jan. 15, l981 describe modulators which consist of two mirrors mounted parallel to and facing each other on a rotating platform. Rotation of the platform varies the optical path length provided the rotation produces a change in the angle of incidence of the incoming beam on the first mirror.
Robert A. Hoult and Charles F. deMey's U.S. Pat. No. 4,621,899 entitled "ASSEMBLY FOR POSITIONING AN OPTICAL ELEMENT" dated Nov. 11, 1986 shows a very accurate system for mounting an optical element on a frame member.
The present invention is directed to improvements over such prior art devices, as will become apparent as the description proceeds.